The subcellular components involved with excitation-contraction coupling processes (sarcoplasmic reticulum, plasma membrane and mitochondria) will be isolated from experimentally induced failing hearts and the release of Ca ions which has been actively taken up by these components will be investigated during the development of cardiac failure. For this purpose, sarcoplasmic reticulum will be incubated in the presence of ATP in media containing methane sulfonate which is impermeable to sarcoplasmic membrane. After the active uptake of Ca ions, S.R. will be washed by medium containing chloride which is permeable to the membrane. This release process in failed hearts will be compared to that of normal hearts. Also, the release of Ca ions taken up actively by cardiac plasma membrane and mitochondria under various experimental conditions will be investigated, during the development of experimental cardiac failure. The plasma membrane and mitochondria will be incubated with ATP in media containing KCl. After the active Ca ions uptake, various amounts of Na ion will be added into the incubation medium to observe Ca ions release. The Ca ions release mechanism in plasma membrane and mitochondria will be compared in preparations obtained from normal and failed hearts. Effort will be directed to ellucidate the causal relationship between the alteration of these Ca ions release mechanisms and the depressed contractility in cardiac failure. BIBLIOGRAPHIC REFERENCE: A modified method for studying the interaction of isolated cardiac cell membrane with ions and drugs. D.H. Kang and K.S. Lee, Analytical Biochemistry 75, 345-355, 1976.